Toxic metals are a significant problem at most Superfund sites, as well as other waste sites and the environment in general. In particular, exposure and toxicity of arsenic (a metalloid) and mercury are timely and important issues, yet the mechanisms by which they elicit their adverse biological effects under conditions of low chronic exposure, such as occur near Superfund sites, are still poorly understood. The toxicity of metals can be traced ultimately to specific interaction(s) with biological molecules, typically cellular proteins. Thus, a major goal of this project is to provide quantitative molecular insight about the interaction of these metals with proteins that appear to be associated with pathways leading to toxicity, based on previous work by this program and others. This research will focus primarily on arsenic and mercury, which have high to very high affinity for sulfur-containing cysteine (Cys) residues in proteins and are found both as inorganic ions (As+3, As+s, Hg+2) and organic species (e.g. monomethylarsenic, methylmercury) in vivo. It is hypothesized that these toxic metals bind selectively to one or more critical Cys residues of a target protein and thereby compromise its biological function, often by affecting the protein structure. For two proteins that appear to be targets for As"1"3 toxicity, the transcription factor Glucoeorticoid Receptor (GR) (Project 2) and the ion transporter Cystic Fibrosis Transmembrane conductance Regulator (CFTR) (Project 8), this project will quantify arsenic binding and characterize its interaction with the protein to provide a molecular explanation for the observed arsenic effect(s) on protein function (e.g. gene expression, ion transport). This project will also quantify the interaction of arsenic and mercury, both as inorganic ions and as various organic species, with key proteins (e.g. metallothionein) and other cellular molecules (e.g. dihydrolipoic acid); these and other data will then be used to develop kinetic/thermodynamic models of the intracellular chemistry of these toxic metals. Finally, this project will determine the distribution, bonding and reactions of these toxic metals with the Cys-rich proteins in hair and nails, with the goal of obtaining fundamental chemical insight that can be used to distinguish toxic metals deposited endogenously (biomarkers for exposure) from exogenous metal contamination in epidemiology studies (Project 4). The overall goal of this project is to provide new molecular and mechanistic understanding about the interaction of arsenic and mercury species with proteins that are putative cellular, targets, involved in metal cellular chemistry, and sites of metal deposition in important biomarkers of toxic metal exposure.